This invention relates to improvements in fluoropolymer containing compositions that are adapted to be used, for example as capstock materials to be coextruded onto various substrates.
Coatings and films made from fluoropolymers are known to possess the property of excellent durability under conditions of exterior exposure. Therefore, it has been desired to use fluoropolymers as a protective cap material for less durable, lower cost materials, particularly thermoplastic polymeric materials such as polvinyl chloride, and pultrusions. However, fluoropolymers have poor adhesion to many polymeric substrates, which has limited the use of fluoropolymers as protective coatings or capping layers. Many attempts have been made to solve this problem, but none have been fully satisfactory. One approach is to employ an intermediate adhesive layer or lamination between the fluoropolymer and the substrate, and examples of this approach can be seen in U.S. Pat. Nos. 4,179,542; 4,317,860; 4,317,861; 4,364,886; 4,415,519; and 4,677,017. Some of these intermediate layers include acrylic polymers. It would be desirable to avoid the additional cost and processing complications entailed by such an intermediate adhesive layer.
U.S. Pat. No. 4,585,701 discloses that adhesion between fluoropolymer-acrylic blends and thermoplastic substrates such as polyvinyl chloride can be improved by incorporating scrap material containing some of the fluoropolymer-acrylic blend into the substrate polymeric mixture. It would be desirable to avoid adding such an additional variable and complication to the extruding process, but instead to achieve adhesion by means of the formulation of the cap stock blend itself.
In order to reduce the melt viscosity of fluoropolymers, another polymer is sometimes blended with the fluoropolymer, particularly acrylic polymers as disclosed in U.S. Pat. No. 3,253,060. Because fluoropolymers are relatively costly, blending it with another resin is also usually advantageous for the sake of lowering the unit cost. Therefore, fluoropolymers used as protective coatings are commonly in the form of blends with acrylic polymers. The fluoropolymer-acrylic blends have heretofore not been found to solve the adhesion problem with respect to polymeric substrates while maintaining adequate impact resistance and processing properties.
Acrylic-styrene-acrylonitrile polymers are known ascapstock materials that are coextrudable with polvinyl chloride to form siding, window and door profiles and the like. Although these materials have adequate adhesion to polvinyl chloride substrates, their exterior durability is not as good as fluoropolymers.